Microchannel classification

Scale-up of microchannel reactors is based on using the optimal channel dimensions rather than seeking the smallest or the largest microchannel. In some cases, the channels may range from 100 pm in hydrauhc diameter to a few millimeters. The classification of a rigorous size range to designate a reactor as microchannel is not necessary. 

Kandlikar, S.G., Microchannels and Minichannels - History, Terminology, classification and current research needs. T Int. Conf. on Microchannels and Minichannels, Rochester, N.Y., April 24-25, (2003). 

Ookawara S, Higashi R, Street D, Qgawa K (2004) Feasibility study on concentration of slurry and classification of contained particles by microchannel. Chem Eng J 101 171... 

As for flow boiling instabilities in classical channels, several types of instabilities have been observed and reported by different authors. Table 2 summarizes these instabilities and their physical consequences on the fluid flow. We also show in the following table which publications reported these instabilities in microchannels. This classification is based on the one proposed for channels by Bergles in 1976 [5] and is divided into two categories ... 

Free surfaces are commonly encountered in many microfluidic applications. One class of free surface microfluidic applications involves individual or discrete drops and sprays, the former being termed digital microfluidics. Another class of free surface microfluidic applications is that which involves two-phase microchannel flows wherein either a gas bubble or stream flows within or adjacent to a liquid stream, a liquid phase flows within an immiscible liquid continuum (i.e., a microemulsion), or a liquid stream stratifies another immiscible liquid stream. These classifications are, however, not mutually exclusive. For example, discrete drops or sprays are not just limited to open microfluidic systems, where they are exposed to an ambient environment. Often, to prevent evaporation, for example, the discrete drops are housed within an oil layer. Alternatively, a liquid spray can be encased within an immiscible liquid medium as a means for generating microemulsions. 

According to the above classification, a channel with its hydraulic diameter less than 490 p,m (at 450 K) is considered to be a microchannel if water is used as a working medium. 

Lab-on-a-Chip Devices for Particle and Cell SeparaUen, Rgure 6 Principle of hydrodynamic filtration, (a) When the flow rate ratios between the side and main channels are low, (b) medium, and (c) high. Broken lines show the virtual boundaries (critical streamline) of the flows distributed into the side and main channels, (d) Schematic diagram showing particle concentration and classification in a microchannel having multiple branch points and side channels. Reprinted with permisiion from [8]... 

---